[Bug fortran/57296] New: Infinite loop in do while when using -O2

[antti.pekka.hynninen at nrel dot gov]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57296
            Bug ID: 57296
           Summary: Infinite loop in do while when using -O2
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: antti.pekka.hynninen at nrel dot gov

Created attachment 30125
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=30125&action=edit
Source code that produces the infinite loop

Gfortran produces an infinite "do while" loop for a very simple code:

    DO I=1,LENIC
       PREF(I)=PIC(I)
       DO WHILE(PREF(I) < -180.0d0)
          PREF(I)=PREF(I)+360.0d0
       ENDDO
    ENDDO

This compiles to something like

L10:
    movsd    (%rbx,%rdx), %xmm0
    ucomisd    %xmm0, %xmm1
    movsd    %xmm0, (%rax,%rdx)
    jbe    L18
L8:
    jmp    L8
    .align 4
L18:
    addq    $8, %rdx
    cmpq    $800, %rdx
    jne    L10


Note that this only happens when pref is allocated using a subroutine:

  subroutine chmalloc(len, p)
    integer len
    real(kind=8), allocatable, dimension(:) :: p

    allocate(p(len))

    return
  end subroutine chmalloc

If I instead use "allocate(pref(lenic))" directly, code works again.

I have added the source code as an attachment, compile with "gfortran -O2
test.f90". My system is Mac OSX 10.6.8.